This invention relates to methods for making polymer products and to novel products made according to the methods.
Polymer products in the form of vascular prostheses conventionally comprise a conduit having varying dimensions and mechanical characteristics which are as close as materials and manufacturing processes will allow to the vessel in the body whose function it is intended that the prosthesis should replace.
A number of tubular prostheses may be grafted into a single vascular system.
There is merit, at least conceptually, in attempting to maintain as much as possible of the host vascular tissue during surgical procedures which involve vascular replacement, principally because there is less alien material introduced into the patient.
Polymer products which comprise a branch and arms emanating therefrom may typically be produced by joining the arms to an independently fabricated branch region. Whilst this procedure has the advantage that it allows the construction of relatively complex branched structures, disadvantages include the product lacking a relatively uniform mechanical consistency; together with a relatively time consuming and thus expensive preparative procedure.
Where a vascular system branches, tubular prostheses may be grafted onto each of the arms comprised thereby. This technique suffers from the serious disadvantage in that it necessitates joints at the increased number of junctions between host and prosthetic vascular material. Consequently, the time spent by the patient under anaesthetic and subject to cardiopulmonary bypass is increased which increases the likelihood of the development of pulmonary and circulatory system disorders, together with the raised possiblilty of cardiac ischaemia, necrosis and infarct.
Moreover, there is a finite possibility that a prosthesis will fail mechanically at the region of its attachment to host vascular material, conventionally regarded as the weakest and most sensitive region of the graft. An increased number of such attachment regions in a single vascular system synergistically increases the possibility of failure of the prosthetic vascular system as a whole.